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THE WILSON JOURNAL OF ORNITHOLOGY • Vol. 123. No. 2. June 2011 
was underway at this locality. Neither nest 
appeared to be on a male territory. Males at 
Cuerici held densely packed territories in open 
shrubby pastures full of cultivated blackberry 
(Rubus spp.). near remnants of oak (Quenus spp.) 
forest. No territories were found in closed canopy 
forest, although both males and females visited 
flowers in these areas. Males at the paramo site 
held small territories at the crest of a hill. 
Territories were small with perches of males 
being within a 15 X 15 m area, and central 
perches of neighboring territories as close as 20 m. 
They were tightly packed as compared to related 
species (CJC, pers. obs.). The males perched in 3- 
10 prominent locations, such as power lines, tips 
of dead twigs protruding from the side of a lone 
tree, or the tip of the tallest cane within a bramble 
patch while on territory. Perches were I to 15 m 
from the ground, and tended to be in sunny 
locations. Males at times moved to shaded perches 
in rare periods of prolonged sun and elevated 
temperatures. 
Most interactions we observed on the territories 
were between males. Intruding males would 
frequently fly onto another's territory. The owner 
would leave his perch and chase the intruder. The 
chase would often, due to the tight packing of 
territories, immediately encroach on a neighboring 
territory, and that bird would join the chase as well; 
•f the chase then entered yet another male's 
airspace, he too would join the fray. The greatest 
number of birds we observed in such a chase was 
tour, accompanied by a tremendous twittering 
Males seemed most active on their territories when 
it was sunny, and arrived on their territories within 
alf an hour of sunrise. In contrast, they departed 
their territories up to 2 hrs before sundown. 
All territories had at least a few plants in flower 
from which we saw the birds feed. The males 
were seen visiting Fuchsia paniculata . cultivated 
Kubus spp.. Comarostaphylis arhutoides . and the 
tiny flowers of F. mien, phytic / on their territories 
oh T- h malcs und fema| c s were also 
bserved visitmg a dense patch of undefended 
fZ \°Z 8 T Spp - in lhe understo >'y of nearby oak 
defended f es fema,CS al San Ge ™rdo both 
efended territories around small dense patches of 
flowering F. paniculata with both attacking other 
onfoZZ I' a \ WC " " * scintilla intruded 
(2 200 m T ^ femalCS at San G <*ardo 
U,200 m us I ) were not observed engaging in anv 
gS' n=r° U,d mdiC: ' K br ^‘» g -h as 
garnering nesting material. 
Vocalizations. —Males uttered a ‘descending 
call (Fig. 2A) as well as a twittering ‘scolding 
call (Fig. 2B) in agonistic interactions with other 
Volcano Hummingbirds. The calls produced were 
directed towards another individual; we did " 
observe undirected vocalizations (i.e.. songs) from 
males on their territories. The descending call was 
also occasionally emitted towards (caged) fe¬ 
males. It consisted of a single tone that started ai 
9.9 ± 0.41 kHz, and descended to 6.8 t 1.4 kHz 
over the course of 1.9 ± 0.6 sec (n = 18 calls 
from 7 males). 
Display Dives. —Males were frequently ob¬ 
served performing display dives throughout the 
day. Two of the males we observed would dive at 
a variety of passerine birds, if they perched 
prominently on the male’s territory, as well as at 
other hummingbirds. Most males did not seem to 
be so indiscriminate, and were only observed 
diving to other Volcano Hummingbirds. It was 
often not possible to ascertain the gender of the 
recipient of the display. It was easy to elicit dives 
Irotn male Volcano hummingbirds by placing a 
caged female on the male's territories, lhe 
majority of males responded to this stimulus by 
performing at least one dive. 
We obtained sound recordings of 87 dives from 
13 males. The dive sound consisted of two 
sounds; a frequency-modulated (FM) tone and a 
series of sound pulses (Fig. 2C). Males began 
producing the FM tone early in the dive, which at 
its initial frequency was 4.07 ± 0.21 kHz In = 
85). and it remained nearly constant pile* 1 
(acoustic frequency) for 0.43 ± 0.17 sec. It was 
then modulated up to 5.80 ± 0.34 kHz (n = S' 1 
over the course of 0.05 sec, then gradually 
descended in pitch to a final frequency ol 4.97 
— 0-31 kHz. The entire sound lasted 0.92 - 
0.20 sec (/i = 85), and a harmonic was present in 
85 of 87 dives. The FM tone was clearly not 
produced by the tail, for one male lacking his tail 
still produced this sound when diving (Fig. 2E1- 
The dive sound also included 2-5 pulses of 
sound (indicated by p in Fig. 2C). These pulses 
were produced at the bottom of the display, as the 
male flew over the target of the display (Fig. 2C). 
and lasted 17 ± II ms (n = 76). The pulses were 
produced 46 ± 9 ms (n = 73) apart; the overall 
rate at which these pulses were produced was 15.2 
± 1 -2 Hz (;i = 76). 
Each pulse consisted of a broad-frequency 
swath of sound reaching up to ~ 12 kHz. A low 
fundamental frequency (0.82 ± 0.29 kHz, 66 
